The invention relates to a two-stroke internal combustion engine in which the fresh gas is led tangentially and upwards in an inclined manner into the cylinder and which instead of a crankcase pump has an additional loader to deliver the fresh gas into the cylinder. Such an internal combustion engine is disclosed in DE-PS No. 454 473.
The internal combustion engine already known is a two-stroke Diesel engine of large volume and slow running. In this engine the scavenging air is led tangentially into the cylinder through several scavenging air ducts. The combusted gas leaves the cylinder accordingly through several exhaust channels that are arranged at the opposite side of the scavenging air ducts.
The internal combustion engine already known cannot work in an optimal manner because a lot of the incoming air directly reaches the exhaust channels instead of first rotating in the cylinder. This leads to a relatively high short circuit loss. In the internal combustion engine already known the rotation of the air is restrained by turbulences and the back-flow in the middle of the cylinder.
The piston with a lug as shown in FIGS. 3 and 4 of the drawing of DE-PS No. 454 473 proves that the inventor had at least guessed at the effect of the short circuit loss. But experience shows that a deviation lug on the piston cannot improve a bad scavenging. This applies to the same extent to the internal combustion engine according to the Austrian Pat. No. 113 633.
Two-stroke internal combustion engines with spark ignition were used until after the Second World War because of their easy construction and their high specific power. Furthermore there is much less NO.sub.x in the exhaust gas of these two-stroke engines than in comparable four-stroke engines which is a result of the mixture of fresh gas and exhaust gas in the cylinder. To gain these advantages, however, one so far had on the other hand to accept a great fuel-consumption and a high portion of CO and HC in the exhaust gas during idle running and in the part-load area. A further disadvantage was the fact that no proper idle running with ignition at each stroke could be reached. This led to a disagreable vibration during idle running speed. Because of these disadvantages two-stroke engines have no longer been used as drive for automobiles for about three decades.
The object of the present invention is to develop a two-stroke internal combustion engine as mentioned at the beginning in such a way that it can work with smooth running and high efficiency as a Diesel engine but also as an internal combustion engine with spark ignition (Otto engine) and that it is more advantageous as far as fuel-consumption and portion of pollutant content in the exhaust gases are concerned than conventional Diesel engines, two-stroke and four-stroke internal combustion engines with spark ignition.
This object is achieved according to the invention by providing only a single sluice with one scavenging port leading into the cylinder and by arranging the sluice at the same side of the cylinder as the exhaust port and next to it.
Due to the arrangement according to the invention the incoming fresh gas forms a rotating drum along the wall of the cylinder. The admission velocity can nearly fully be converted into a rotary motion so that the fresh gas vortex rotates at a high speed. Since the intake duct is inclined in direction of the combustion chamber the fresh gas reaches the combustion chamber on a defined way even in case of low rotational speed and can be safely ignited when petrol is used. Tests with this scavenging resulted in a smooth idle running in case of very low rotational speed and in a perfect ignition at each stroke.
In spite of its functional advantages the construction of the internal combustion engine according to the invention is much easier than that of conventional two-stroke engines because its basic structure--crankshaft, crankcase, lubrication--is that of a four-stroke engine and the cylinder wall only has two openings, i.e. the exhaust port and the scavenging port. Thus also a multicylinder engine of simple cast technic with small cylinder distances can be produced.
Due to the arrangement according to the invention one does--contrary to the prior art--achieve an optimal scavenging of the combusted gas especially in the partload area and avoids a mixing of fresh gas and residual gas. It is the object of the invention to completely separate the fresh gas from the residual gas in order to reach a laminated charge and lean operating even in case of little partial load. The arrangement according to the invention is the only means to achieve this object in the easiest possible way.
The flow in the sluices has especially little loss if according to an advantageous embodiment of the invention they are running mostly straight-lined and are narrowing towards the cylinder. Furthermore this arrangement leads to a particularly high rotational speed of the fresh gas vortex.
It is also advantageous if a back-flow stop in the form of non-return valves is provided between the loader and the sluice. This prevents a back-flow of combusted gas from the cylinder into the loader. Such non-return valves can for example be leaf-valves such as they are used nowadays on the intake side of some conventional two-stroke engines. They open automatically once the pressure in the cylinder is falling below that of the loader. Besides they have so little flow-resistance that they do not restrain the gas-flow and do not require an additional power consumption.
According to another advantageous embodiment of the invention one can instead of a non-return valve provide a stopping device that is driven by the internal combustion engine either direct or according to a programme. It is particularly convenient if the stopping device is a rotary slide valve. Such rotary slide valves are especially advantageous in the case of multi-cylinder engines. This rotary slide valve is made as known in such a manner that the fresh gas enters the duct at a front end and flows through this duct towards the control openings. The rotary slide valve can be driven by toothed belts, chains or gears.
The drive of the rotary slide valve is particularly simple if the rotary slide valve is arranged parallel to the crankshaft.
A control element such as it has for example been developed by the firm Pierburg for the shifting of camshafts is inserted between the rotary slide valve and the drive. Thus the delivered air is adapted to the requirements of the engine in an optimal manner and a usual choke control is no longer necessary.
The adjustment is carried out automatically by means of an electronic control element which processes load, rotational speed, pressure and temperature. This control element can be combined with that for the ignition point and the fuel injection so that in that case also the air volume and air mass are further factors of influence. The replacement of the usual choke control by the control edge of the rotary slide valve ensures that when the control edge of the rotary slide valve is opened the full load pressure always causes a high speed of the fresh gas in the passage way. Besides it is possible to completely close the control opening when running downhill by pushing force so that a saving of fuel is reached.
In the case of petrol injection and its cut-off during the pushing force phase the electronic can also produce a higher throughput of air and by a higher compression work in the cylinder and in the loader a quicker slowing-down of the motor speed.
It is also of advantage if the scavenging port is opened by a greater crank angle than the exhaust port and if the lower edge of the scavenging port is considerably higher than the controlling upper edge of the piston in the bottom dead centre. In such an arrangement the fresh gas can flow for a longer period from the upper edge of the piston into the cylinder without being influenced.
Although Swiss Pat. No. 268 279 shows spill ports the upper edges of which are arranged higher than those of the exhaust ports such an engine cannot run because such an arrangement of the ports is only useful in the case of forced loading. The spill-slide described in the same patent is also useless because the patent expressly concerns a two-stroke engine with crankcase scavenging. In two-stroke engines with crankcase scavenging it is necessary that when the piston goes down after opening of the spill ports combusted gas presses into the crankcase which leads on the one hand to higher pressure and on the other hand to a spilling later on. Two-stroke engines with a crankcase pump and spilling that is not controlled mechanically anyhow work "unsymmetrically" when the gas is changed and can be so much deteriorated by the devices according to Pat. No. 268 279 that they are unable to run by themselves.
If the combustion chamber is built as an annular channel the structure of the internal combustion engine is simple and high thermal loads are prevented. But the combustion chamber can also be built in form of a disk or in a form that is between a disk and an annular channel.
It is also advantageous if in the embodiment as Otto engine the sparking plug is provided at the outside of the combustion chamber periphery because the mixture rotating there is particularly easy to ignite so that the ignition is reliable even in case of low rotational speed. Thus a two-stroke Otto engine is realized that has the advantages of a usual two-stroke engine but not the disadvantages of a bad efficiency, a bad true running in the part-load area and a high portion of pollutant content in the exhaust gases.
The ignition is particularly reliable if according to another embodiment of the invention two sparking plugs are provided staggard by 180 degrees at the outside of the combustion chamber periphery.
In order to remove remaining unbalances of the crankshaft drive the rotary slide valve can at the same time be formed as compensating shaft.